The immune response to Shope fibroma induced tumors in the rabbit will be further characterized. Studies carried out during the preceding grant period indicate complex immune reactivity in the normal adult rabbit including direct T cell cytotoxicity, natural cellular cytotoxicity, antibody dependent cell mediated cytotoxicity, development dependent antibody cytolysis and an absence of blocking factors. Immune response profiles will be further studied in animals that resist the growth of fibromas (adult domestic rabbits) as well as in animals that exhibit progressive growth and generalized fibromatosis (newborn domestic rabbits, adult cottontail rabbits and "immunosuppressed" adult domestic rabbits). Immune products will be assayed for reactivity to specific antigen by in vivo and in vitro neutralization tests as well as by target cell cytotoxicity and mixed lymphocyte tumor reactions using cultured fibroma cells and SFV infected rabbit kidney cell monolayers. Non-antigen specific changes will be monitored using T and B cell markers, mitogen responses and in vitro PFC responses. Whole and fractionated lymphoid cells and serum antibody will be analyzed by passive transfer in vitro and in vivo. These studies should clarify the role of immune products in determining the growth and dissemination of SFV induced tumors.